1. Field of the Invention
The present invention generally relates to fuses and more particularly to a capacitor fuse structure.
2. Description of the Related Art
Conventional systems utilize fuses in semiconductor chips to provide redundancy, electrical chip identification and customization of function. For designs having three (or more) layers of wiring, the fuses are typically formed from a segment of one of the wiring layers, e.g. the xe2x80x9clast metalxe2x80x9d or xe2x80x9clast metal minus onexe2x80x9d wiring layer. Fusing (i.e. deletion of a segment of metal fuse line) is accomplished by exposing the segment to a short, high intensity pulse of xe2x80x9clightxe2x80x9d from an infra-red laser. The metal line absorbs energy, superheats, melts, expands, and ruptures any overlaying passivation. The molten metal then boils, vaporizes or explodes out of its oxide surroundings, disrupting line continuity and causing high electrical resistance. A xe2x80x9csensingxe2x80x9d circuit is used to detect fuse segment resistance. Sense circuits can be designed to xe2x80x9cunderstandxe2x80x9d that fusing has occurred when line resistance increases or line resistance decreases.
Because of line to line coupling which slows signal propagation, there is a trend for the inter level dielectric (ILD) to be comprised of polyimide nanofoams or porous glass. These dielectrics are of a class characterized by having low dielectric constant (K). They are not solid materials and will be damaged or collapse under standard laser fuse blow conditions, leading to unreliability and possibly yield degradation of the integrated circuit device.
To improve signal propagation, high conductance materials, e.g. copper, silver, etc., may be used to define device wiring lines (conductors). More specifically, electrical resistance is reduced by using copper or other high conductance materials. Several of the common high conductance materials corrode easily and if fuse structures are formed from segments of wiring lines, corrosion and the attendant degradation of device reliability can be expected if the blown fuse is left exposed.
Also, conventional laser blowing (or even electrical blowing) may damage the fragile, porous ILD, causing it to collapse and change its dielectric constant. The laser fusing could also release particles of copper into the porous films, presenting potential reliability concerns and possibly compromising the basic local structural integrity of the chip.
Therefore, there is a need for a new type of fuse structure which can be blown (e.g., opened) without suffering the reliability problems associated with conventional fuses.
It is, therefore, an object of the present invention to provide a corrosion insensitive structure and method for a programming device or a fuse that includes a capacitive circuit having a capacitance which is alterable. The capacitive circuit can include a first capacitor, a fuse link connected to the first capacitor and a second capacitor connected to the fuse link, wherein removing a portion of the fuse link changes the capacitance.
The first capacitor includes a first top plate and the second capacitor includes a second top plate. The first top plate, the second top plate and the fuse link are positioned in one planar conductive level within the device. The structure also includes an insulator over the fuse link. The fuse link has a length greater than a spot size of the energy light source used to open the insulator. The invention also includes a sensing circuit for detecting a change in the capacitance. The first capacitor and the second capacitor can be stacked capacitors, inter-digitated capacitors or parallel spiral patterned capacitors.
The invention also includes a process for programming a capacitive device having a first capacitor and a second capacitor connected by a fuse link. The process includes removing an insulator above the fuse link and etching the fuse link. The etching comprises one of wet etching and dry etching. The insulator can be removed using light energy, such as laser and ultra violet light. The light energy is below an energy level required to delete the fuse link. The method may also include sensing a change in capacitance of the capacitive device.
In another embodiment, the invention is a process for programming a capacitive device having at least two inter-digitated capacitors. The process alters an insulator above one of the inter-digitated capacitors to change a capacitance of the device. Such altering can include densifying or removing the insulator by applying one of a laser and ultra violet light to the insulator. Also the process can include sensing a change in capacitance of the device.
Another embodiment of the invention is a semiconductor fuse including a capacitor having a first and a second node (the first node being electrically connected to a sensing circuit for sensing a change in capacitance, and the second node being electrically insulated from ground by a narrow dielectric filled gap device), and a charge collection plate for charging the capacitor, coupled to the second node of the capacitor. The capacitor includes two parallel plates separated by a dielectric layer. The narrow dielectric gap device can be conductive lines separated by a dielectric material or a field effect transistor. The capacitor could be a silicon trench capacitor.
Yet another embodiment is a method of fusing a semiconductor device, which includes providing a capacitor having a first and a second node (the first node being electrically connected to a sensing circuit for sensing a change in capacitance, and the second node being electrically insulated from ground by a narrow dielectric filled gap), providing a charge collection plate coupled to the second node, and inducing a charge across the first and second node of the capacitor sufficient to electrically break down the narrow dielectric gap.
With the invention, a circuit may be programmed by altering its capacitance. Further, the invention opens fusible links using an etching process which substantially reduces or eliminates the possibility of affecting structures adjacent the fusible link. This structure and process is superior to conventional fuses because very low level energy sources such as a low power laser, ultraviolet light or a reactive ion etching process can be utilized to blow the fuse. The energy level utilized by the invention does not cause the fuse material to explode or boil as conventional fuse and processes do. Therefore, blowing the fuse does not damage the surrounding dielectric material. Further, if any of the fuse material remains, it will not corrode or detract from the reliability of the remaining circuit.
Thus, the invention expands the usefulness of programmable and fusible devices and increases the manufacturing yield of circuits which include such devices.